Method of varying the thickness of a glass sheet while on a molten metal bath



OC- 3. l967 E. R. MICHALIK ETAL 3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTEN METALBATH I Filed Jan. 16, 1963 6 Sheets-Sheet l Oct. 3, 1967 E. R. MICHALIKETAL 3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLT'ENMETAL BATH 6 Sheets-Sheet 2 Filed Jan. 16, 1963 FIG.3

FIG

INVENTORS fava/vo ,Q Mfr/MHK@ Bcfoeof n( CL 3, 1967 E. R. MICHALIK ETAL3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTEN METALBATH Flled Jan 16, 1963 G Sheets-Sheet 5 Fia.

INVENTORS Hwa/m e www1/KQ? m6519265 W/W/ssQ/V OGL 3, 1967 E. R. MICHALIKETAL 3,345,149

METHOD OF VARYI NG THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTENMETAL BATH 6 Sheets-Sheet 4 Filed Jan. 16, 1963 vF'ICLS FGJO INVENTORSfMaA/a e wc/maxi( @meer #KM/ssa# #from/ff @CL 3, w67 E. R. MICHALIK ETAL3,34549 METHOD OF VARYING THE THICKN'SS OF A GLASS SHEET WHILE ON AMOLTEN METAL BATH Filed Jan. le, 196s V e sheets-sheet 6 2W. N $0 NrsE/S EWMM wif n a n E P wm E 0m. L E U GY w B .um M w u u R E P m U D o M/jM/llsm PRSSURE wm-sm FLOAT CHAwmER ATTORNEY United Statesv Patent O3,345,149 METHOD F VARYING THE THICKNESS 0F A GLASS SHEET WHTLE 0N AMOLTEN METAL BATH Edmund R. Michalik, West Miliiin, and George W.Misson, Pittsburgh, Pa., assignors to Pittsburgh Plate Glass Company,Pittsburgh, Pa., a corporation of Pennsylvania Filed llan. 16, 1963,Ser. No. 251,848 l 4 Claims. (Cl. 65-99) This application relates to themanufacture of flat glass by floating glass on a liquidk bath, such asmolten metal, so that the resultant flat glass has fire-finishedsurfaces requiring little or no additional surfacing for ultimate use.

lt has been proposed heretofore to produce flat glass by floating aribbon or sheet of glass upon the surface of a bath of molten metal. Theproduct produced by this process has surfaces which differ somewhat fromeach other. The top surface thereof, because of the heat involved, has afire-finished surface. The bottom of the ribbon in contact With themolten metal is ilat and has a surface having a similar appearance to afire-finished surface.

When producing oat glass of compositions approaching that of commercialplate and Window glass or similar soda-lime glasses and using a moltenmetal such as a bath of tin or tin alloy, molten glass poured directlyonto the bath of metal ultimately will attain an equilibrium thicknessof approximately 1A inch (hereinafter sometimes called equilibriumthickness), IEven a preformed ribbon of glass of a thickness differentfrom the equilibrium thickness when remelted While supported on themolten metal, will nevertheless seek the equilibrium thickness.Heretofore, when thinner glasses were desired, it was considerednecessary attenuate the ribbon of glass While in molten condition toproduce thicknesses of glass differing from the equilibrium thickness orto subject a stiffened ribbon or sheet of dilferent dimension to only asurface melting treatment. To elfect attenuation, traction elementscontacting the glass at its marginal edges to maintain ribbon widthduring attenuation are required. Considerable edge trim is thus requiredbecause of the necessary Width of the traction elements to chill theglass edges and maintain a substantially constant ribbon Width.

The need for glass of thicknesses different from the equilibriumthickness is great. For example, the majority of laminated glassassemblies useable in the automotive industry are constructed of twopieces of glass of a thickness less than the equilibrium thickness(usually of the order of 1)/16 or 1,@ inch) with a layer of plastic4sandwiched therebetween. According to the invention described in thecopending application of Edmund R. Michalik, Ser. No. 188,664, filedApr. 19, 1962, now abandoned it has been found that glass ofconventional plate and Window composition and of a desired thicknessdifferent from the described equilibrium thickness can be produced byfloating a sheet or ribbon of glass on the surface of a molten bath ofmetal such as tin or tin alloy having a density greater than that of theglass and holding the glass at a melting temperature while modifying theapparent weight density of the glass with respect to the Weight densityof the metal of the bath, e.g., by changing the degree of immersion `ofthe glass in the metal. Thus, it has now been found that when the glassdisplaces a greater quantity of metal than that usually displaced undernormal atmospheric conditions, the molten glass tends to stabilize at athinner thickness than the equilibrium thickness and vice versa. Thus,modifying the degree of immersion of the glass in the metal results in amodification of the amount of metal displaced by the glass which may begreater or less than For most purposes, it is found preferable to applythis different fluid pressure `only to a portion of the surface of theglass sheet and to leave a margin, generally a pairv of opposed margins,of the glass sheet exposed to another fluid pressure which rnay be thesame as or different from that applied to the metal surface at the glassedge. As a result, of course, the margins diifer in thickness from theportion to which the dilferent fluid pressure is applied. In practice,assuming the glass is sufficiently hot to freely flow, and ignoringtransient conditions, there need be no actual change in metaldisplacement. Rather, the metal level may remain the same but the massof glass floating upon it, i.e., displacing it, Will be diminishedbecause the glass exposed to the increased fluid pressure becomesthinner.

By selecting the magnitude of the pressure on the central areas of theglass and supplying a ribbon of desired thickness to the bath, themaintenance of this desired glass thickness is insured. If a ribbon of athickness other than that which is desired is supplied to the metalbath, then, because of the character of molten glass to flow, a ribbonof the desired thickness can be produced by proper selection of thepressure which modifies the apparent densities of the glass with respectto the bath. Because of the temperature involved, the glass attainssurfaces characteristic of lire-finished surfaces, so that little o-r nosubsequent abrasive surfacing is required for ultimate use.

When the treated glass is cooled sufliciently, it is withdrawn from themetal bath without surface damage due to equipment contact, as byapplying only a tractive force to the glass ribbon. Since attenuation ofthe glass becomes less important in accordance with the teachings of theaforesaid applicati-on, special apparatus within the contines of themetal bath or contiguous thereto to contact the glass surfaces is notrequired in contrast to previous processes.

The present invention is directed to improved methods and apparatus forproducing glass according to the invention described and claimed in theaforesaid copending application. It is also directed to improved methodsand apparatus for producing glass according to the inventiondescrbed andclaimed in the copending application of Edmund R. Michalik and George W.Misson, Ser. No. 191,833, filed May 2, 1962, now Patent No. 3,241,937,which invention is directed to methods and apparatus for maintaining aditerent fluid pressure above separate portions of a floating glassribbon.

According to an effective method of practicing the present invention, aribbon of glass is presized as to thickness and width by convenientmeans, such as by passin-g molten glass through a slot or between sizingrolls and cooling the ribbon to stabilize its dimensions. This ribbon isthen passed to a pool of molten metal having a greater density than thatof the ribbon and the ribbon is oated on the surface of the metal duringits movement thereacross. A super-atmospheric pressure is applied tothe" upper surface of a central area of the ribbon while the temperatureof the ribbon is raised to a melting temperature. After the surfaces ofthe ribbon have improved, i.e., smoothed out, and surface defects havebeen elimi- I nated or reduced in magnitude or number, the ribbon `iscooled to a stiffened state and is removed from the metal.

Such a super-atmospheric pressure may be applied through a largepressure chamber above the ribbon with adequate marginal seals toseparate the pressure chamber from the atmosphere adjacent the ribbonedges and bath while allowing free movement of the ribbon beneath thechamber. An effective fluid seal can be achieved in accordance with thepresent invention by providing a plurality of separate, relativelysmall, fluid pressure zones around the periphery of the pressure chamberbetween the lower surface of the walls of the chamber and the underlyingglass ribbon. Each zone is formed by an individual ow of gas from areservoir under higher pressure, the flow being throttled between thereservoir and each zo-ne to restrict the passage of gas between the two.The gas may be throttled to different zones in a nonuniform manner toprovide zones of dilerent pressures and thereby control the manner inwhich the seal functions. Within each zone, gas entering from thereservoir is diffused after throttling so as to avoid creation oflocalized jets normal to the glass ribbon. Provision may be made for theescape of the flow of gas emanating from each zone through passagewaysinterspersed throughout the pressure bed.

Alternatively, the super-atmospheric pressure applied to the uppersurface of a central area of the ribbon may be provided in its entiretyby a plurality of separate, relatively small, fluid pressure zonescreated in close proximity to the ribbon throughout the central area.This arrangement not only eliminates the need for a separate edge sealsurrounding the pressure area, but also allows the pressure exerted uponthe upper surface of the ribbon to be varied both across the width andalong the length thereof. It is thereby possible to quickly bring aribbon to a desired thinner dimension by applying an initial pressuresubstantially in excess of that which would establish the desiredthickness by supplying the zones adjacent the most recently formedportions of the ribbon with a greater pressure than zones positionedfarther along the ribbon. It is also possible to produce a ribbon havinga transverse wedge shape or other varying configuration with thisarrangement. Thus, the pressure exerted upon the upper surface of thecentral area of the ribbon may be varied from one side to the other,either progressively or in stages, to create a corresponding thicknessvariation. In lieu of separate pressure zones, a po-r-ous plate throughwhich gas under pressure may be emitted and having exhaust channelsinterspersed throughout can be used adjacent the upper surface of theoating ribbon to exert a fluid pressure.

The attendant advantages of this invention and the various embodimentsthereof will be readily appreciated as the same become better understoodby reference to the following detailed description when considered inconnection with the accompanying drawings in which:

lFIG. 1 is a longitudinal section of an apparatus for producing glassaccording to the inventive process herein contemplated showing means forapplying a super-atmospheric pressure to the top of a ribbon of glasssupported on a molten metal bath and for dividing the apparatus intoseparate pressure chambers;

FIG. 2 is a horizontal, sectional view, with parts omitted, taken online 2-2 of FIG. 1 looking in the direction of the arrows showing themeans for providing a plurality of pressure zones between the glassribbon and a wall separating a central pressure chamber from thesurrounding portion of the apparatus',

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1 and in thedirection of the arrows partly showing a seal for separating theatmosphere within the apparatus from the surrounding atmosphere;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 1 and in thedirection of the arrows showing structure at the entrance end of themolten metal tank for controlling the level of the liquid metal.

FIG. 5 is a sectional view taken on line 5-5 of FIG. 1

and in the direction of the arrows showing the surfacing zone, tank wallconstruction, and a Huid seal constructed in accordance with the presentinvention for separating a pressure zone above a central portion of afloating ribbon from the surrounding zone within the apparatus;

FIG. 6 is a sectional view taken on line 6-6 of FIG. 1 and in thedirection of the arrows showing the molten metal level control structureat the exit end of the molten metal tank;

FIG. 7 is a sectional view taken on line 7-7 of FIG. 1 looking in thedirection of the arrows showing the exit seal of the molten ymetal tank;

FIG. 8 is an enlarged view, partly in section, of the uid pressure sealarrangement taken along line 8-8 of FIG. 2 looking in the direction ofthe arrows and schematically indicating the principal flows of gas;

FIG. 9 is a partial horizontal view of the pressure seal arrangementtaken along the line 9 9 of FIG. 8 looking in the direction of thearrows;

FIG. 10 is an enlarged view similar to FIG. 8 but showing a secondembodiment of a uid pressure seal arrangement and schematicallyindicating the principal flows of gas;

FIG. 11 is a partial horizontal View of the uid pressure seal embodimentof FIG. 10 taken along the line 11-11 of FIG. 10 looking in thedirection of the arrows;

FIG. 12 is a longitudinal section of another apparatus for changing thethickness of a oating glass ribbon showing means for selectivelyapplying a super-atmospheric pressure to the top of a ribbon of glassusing a plurality of closely adjacent uid pressure zones above theribbon;

FIG. 13 is a horizontal, sectional view taken along the line 13-13 ofFIG. 12 looking in the direction of the arrows, schematically showing inphantom the individual chmaber means in modular arrangement for applyinga super-atmospheric pressure to the top of a floating ribbon;

FIG. 14 is a view partly in section taken along the line 14-14 of FIG.12 showing in end elevation a modular arrangement of pressure chambersand a plenum for supplying gas thereto positioned above a floatingribbon of glass;

FIG. 15 is a horizontal view taken along the line 15-15 of FIG. 14looking in the direction of the arrows showing in detail the modulararrangement of chambers for producing pressure zones above the glassribbon;

FIG. 16 is a sectional view of the chambers taken along the line 16-16of FIG. 15 looking in the direction of the arrows, schematically showingthe ow of gas from the chambers to the upper surface of a oating ribbonand includes a diagrammatic pressure graph;

FIG. 17 is a bottom plan view similar to FIG. 15 but showing a differentembodiment including a porous plate and exhaust passageways therethroughfor providing a uid pressure above a floating ribbon of glass; and

FIG. 18 is a view partly in section of the apparatus shown in FIG. 17taken along the line 18-18 and looking in the direction of the arrowsand schematically indicating the ow of gas.

With particular reference to the drawings, in FIG. 1 there is shown apair of forming rolls 12 at the delivery end of a glass melting furnaceof conventional construction (not shown) to form a ribbon of glass 14which is delivered onto an apron arrangement 15 and thence onto thesurface of a bath of molten metal 16 contained within a tank 18. Themolten metal has a density greater than the glass ribbon 14, so that theribbon oats on the surface of the molten metal. The metal may be tin, analloy of tin, or the like.

In order to maintain the metal of the bath 16 in molten condition,thermal regulating means, such as electrodes 20 may be located in thefloor of the tank 18, as illustrated, or may be submerged within themolten metal, so as to affect the temperature of the bath. Theelectrodes 20 are connected to a suitable source of power (not shown) ina conventional manner. Each electrode may be individually energized andcontrolled, so as to provide a desired thermal gradient within thevarious sections of the tank 18, as will be described. The glass ribbon14, after treatment within the tank 18, is withdrawn from the tankwithout injury to its surfaces by traction or pinch rolls 22 onto aroller conveyor 24.

The tank 18 is constructed of a refractory bottom portion 26 and arefractory top portion 28, joined and sealed together, except for anentrance 18a and an exit 18h, by a suitable sealing means 29 (FIG. 3).The sealing means illustrated is of a bellows type and permits the topportion 28 of the tank to be raised from the bottom portion 26 forrepairs, etc., without the necessity of removing refractory parts andthe subsequent repair of removal parts. The bottom portion 26 containsthe molten metal 16 and is subdivided into an entrance zone 26a, aheating zone 26b, a surfacing zone 26e and a cooling zone 26d. Thesezones are defined by submerged walls or baffles 38a, 30h, and 30e, sobuilt to materially reduce convection currents inthe molten metalbetween the various zones. Other submerged baflles 32 are in the coolingzone to control convection currents in that zone. The level of the metalof the bath is controlled by level control weir 34 at the entrance endof the tank 18, a level control weir 36 at the exit end of the tank, andby an inlet 38. Preferably, the metal level is always maintained so thatthe glass ribbon being treated remains free of contact with anysubmerged wall or bafiie within the tank 18. The inlet 38 (see FIG. 5)is located through a Wall of the tank 18 and is connected to a suitablesource of molten metal to supply molten metal to the tank 18.

VThe space between the top portion 28 and the surface of the metal poolis divided into two vchambers 28a and 28b by the front side of acircumferential wall 40. This wall depends from the roof 28 and has itsside sections spaced from the walls of tank 18, thereby providing a gasspace 28e along each side of the tank. This gas space 28C may in effectbe a continuation or extension of chamber 28a.

A gas which is inert to the components of the bath, such as nitrogen orthe like, is introduced, under pressure, into each gas chamber orpressure zone, through conduits 42 and 44, each connected to a suitablesource of the pressurized gas (not shown). The gas is preferably heated,so as to eliminate chilling of the zones and the glass being treated.The pressure at which the gas is introduced into the zones 28a and 28Cis different from the pressure of the gas introduced into the zone 28h,as will be later described in detail. The pressure zone 28b may befurther subdivided by Walls or baffles 46a, 46b, 46c and 46d fortemperature control purposes.

Radiant heaters 48 are located adjacent the roof of the tank 18 tomaintain the desired glass temperature between the exit and entranceends of the tank. These radiant heaters 48, located in both pressurezones, as illustrated, are connected in a conventional manner to asource of electric power (not shown) and may be individually controlledfor temperature :gradient control. The control means is any conventionalcontrol means and need not be ldescribed and shown in detail. Ifnecessary, cooling means can be located above the cooling zone to insurethe proper temperature of the glass being removed from the bath.

In order to prevent the leakage of the inert gas from the zones Withintank 18 to the outside atmosphere, pressure seal arrangements 50 and 52,as disclosed in the aforementioned copending application Ser. No. 191,-833, are provided at the entrance and exit ends, respectively, of thetank 18. Each includes a plurality of grooves 66 (FIGS. 2 and 3) andinert gas is supplied to the upper seals through pipes 62 and to thelower seals through plenum chambers 70 (see FIGS. 1 and 3), both havinga plurality of orifices, not shown in the pipes but indicated at 72inthe plenum chamber, for emitting inert gas upgler pressure. Thedischarged gas, flowing across the lands and grooves minimizes thetransfer of gas be- 6 tween the chambers in the top 28 of tank 18 andthe outside atmosphere.

The apron arrangement 15 may take several forms without departing fromthe spirit of the invention. For example, it many include a conventionalseries of rollers, as illustrated in United States Patent No. 1,954,077to Gelstharp, or it may be a slip table, as illustrated in United StatesPatent No. 1,657,212 to Hitchcock.

Means are provided for controlling the level of the molten metal in thebath 16 and may include, as illustrated, the weirs 34 and 36 and theinlet 38. The weirs 34 and 36 are plates of a refractory materialslideable within slots formed in the tank refractory parts. The weirsare vertically adjustable by suitable means, as screws 34a and 36a,respectively (FIGS. 4 and 6), so as to adjust the molten metal level,depending upon the thickness of glass being produced. Each Weir definesone side of a trough 34b and 36h, respectively, the other sides andbottoms of the troughs being defined by walls of the tank or othersuitable refractory material. Conduits 74 and 76 pass through the wallsof the tank 18 and communicate at one end with the troughs 34h and 36h,respectively. Each conduit is connected to discharge molten metal into asump (not shown) for regeneration and reheating and from which moltenmetal is pumped to the tank 18 through the inlet 38. Each conduit 74 and76 is provided with a trap, i.e., a U-bend in the conduit, so as toprevent the entrance of atmospheric air into the tank 18 which wouldcause oxidation of the metal of the bath.

Referring now to FIGS. 2, 5, 8 and 9, there is shown means for providinga very effective fluid pressure seal between the lower surface ofcircumferential wall 40 and the upper surface of the ribbon of glass 14.The purpose of this seal is to restrict the flow of gas from chamber2812 to chambers 28C, which are at a lower pressure. The more effectivethe seal is, the more uniform is the pressure applied to the centralarea of the ribbon. This is because any flow of gas from within chamber2812 to chambers 28e reduces the static pressure exerted upon the glass.Thus, if leakage occurs, the pressure profile across the ribbondecreases from the center to the margins and becomes bell-shaped ratherthan square, notwithstanding the fact that the volume ofl gas exertingthe pressure within chamber 28b may be maintained constant bycontinually replacing escaped gas.

In order to achieve an effective seal, a plurality of individuallysupplied pressure zones are provided directly beneath wall 40. To thisend, a fiat, modular bed of chambers 80, each chamber or module beingsmall with respect to the length and width of the dividing wall and inclose juxtaposition, each to the other, is provided beneath wall 40. Inthe embodiment of FIGS. 5, 8 and 9 all modules 80 have their lowertermini of rectangular configuration and lying in a common plane. Themodules 80 are arranged in successive rows crossing the intended path oftravel of the ribbon and extending along the wall 40. Preferably therows are at an angle from the direction of ribbon travel, as illustratedin FIGS. 2 and 9. Each module shown is subdivided into separate chambers88a, 80b, 80C and 80d, each individually supplied with gas throughorifices 82.

Each module 80 has a hollow stem 84 of smaller cross sectional area thatthe outer terminus and each opens into a plenum chamber positioned abovethe module bed and acting as a support therefor. Each module of thisembodiment is substantially enclosed, except for the lower, open end,and separated from other modules by an eX- haust zone 86 communicatingwith larger exhaust channels 87 between the module stems. Communicationbetween the exhaust Zones 85 and the pressure chamber 28h is preventedby barrier plate 83 along the inside row of modules 80. Barriers 88separate the plenum chamber into independent sections and inert gas,such as nitrogen, is fed to the independent sections through pipes 89from a source not shown. The modules and plenum chamber are in mostcases made of metal or refractory material that will withstand highoperating temperatures.

The embodiment shown in FIGS. 10 and 1l may also be used to create aplurality of independent pressure zones beneath wall 40. A plurality ofmodules 90 are provided, contiguous with each other and each suppliedthrough a separate orifice 92 in direct communication with a plenumchamber 94. In this embodiment, no exhaust passages are provided betweenadjacent modules.

In the operation of this device illustrated a ribbon of glass is formedby passage of molten glass between a pair of forming rolls 12 from asource thereof, such as a conventional glass melting tank, and theribbon 14 is delivered to the front section of the tank 18 passingthrough the front or entrance seal 50.

Gas which is inert to the metal is fed into a pipe 62 and flowsdownwardly impinging against the glass and thereby isolates the interiorof the tank 18 from the outside atmosphere. A similar gas is supplied tothe plenum chamber 70 under pressure high enough to cause the gas inthis chamber to flow through the orifices into the grooves 66 and tohold the ribbon away from the solid parts of the tank.

In general, this gas is preheated by means not shown to a temperaturesuciently high to prevent undue cooling of the glass. Normally, thetemperature of the gas supplied to pipe 62 and chamber 70 will be above500 to 1000 F. and often in the range of 1400 F. up to a meltingtemperature of the glass.

After the ribbon 14 has entered chamber 28a it is laid upon the surfaceof the molten metal and is led through the modular fluid pressure sealinto chamber 28b which is at a higher pressure than chambers 28a and23C.

As shown in the drawings, the ribbon 14 has a width greater than thatenclosed by the wall 40, thus providing a narrow margin which extendsbeyond the edges of the wall 40 into the chambers 28C. Sealing gas isdelivered from modules 80 or 90, the outer termini of which are narrowlyspaced from the upper surface of the ribbon. The spacings contemplatedherein are on the order of 0.001 inch to 0.10 inch or greater. Gasemitted from the modules is caused to impinge against the edge portionof the ribbon 14 that is immedaitely below the walls 40, therebyseparating the chamber 28b from 28e by a gaseous curtain. The gas issupplied at a pressure sufiicient to maintain the pressure differentialbetween the chambers.

This curtain or fluid pressure seal is comprised of a plurality ofindividually supplied pressure zones that function independently fromone another. The independent functioning is assured by supplying eachseparate charnber from a separate orifice. FIGS. 8 and l0 schematicallyindicate the principal ows of gas. The relatively small size of orifices82 or 92 provides a drop in gas pressure from the plenum to the interiorof the modules. Not only are slight variations in plenum pressureminimized thereby, but also the gap between the lower terminus of eachmodule and the upper surface of the glass ribbon becomes self-adjustingto a uniform spacing about the entire periphery of each module or, ifdivided, each submodule. This occurs because any decrease in the gapresults in a buildup of pressure within the module cavity, therebyexerting the necessary force, as great as the plenum pressure, ifnecessary, to move the ribbon away from the module, As this occurs, thegap becomes larger and the pressure within the module cavity is reducedby the escape of gas through the larger gap. To be responsive tolocalized changes in spacing that do not occur along the entire ribbonmargin, it is necessary that the modules be relatively small withrespect to the length and width of the wall 40. For this reason smallchambers, such as 80a, 8017, 80C and 80d function extremely effectively.However, as long as the module size is kept small, on the order of oneto two inches across, it is generally not necesary that they besubdivided. Various module designs and their construction suitable forproviding the pressure seal contemplated herein are disclosed in the-copending application of James C. Fredley and George E. Sleighter, Ser.No. 139,901, filed Sept. 22, 1961, now abandoned and the copendingapplication of George W. Misson, Ser. No. 236,- 036, tiled Nov. 7, 1962,now Patent No. 3,223,500.

Internal pressure within chamber 28b may be most effectively maintained,particularly in the absence of eX- haust zones within the fluid curtainas in the embodiment of FIGS. l0 and l1, by varying the pressure in themodule chambers across the width of the pressure seal. That is, if themodules positioned most closely adjacent the interior of pressurechamber 28 exert an inward pressure approximating that within thechamber, there will be no outward flow of gas from chamber 28b. If themodules toward the outer portion of Wall 40 exert progressively lesspressure, the tlow of gas from the pressure seal will be substantiallyentirely outward of pressure chamber 28b A substantially staticcondition within chamber 28b is thereby achieved completely across thewidth to the very inside edge of the fluid pressure seal and thepressure upon the entire -portion of the ribbon beneath chamber 28bremains constant. Of course, this would not be possible if the spacingbetween the ribbon and the modules could not be maintained constant, asin the manner facilitated by the self-adjusting feature of the modules.

The pressures exerted by the various modules may be conveniently variedin whatever manner desired by varying the size of the orifices 82 or 92.Thus, for greater pressure in those modules at the inner edge of wall40, the orifices 82 or 92 should be relatively large. However, thepressure in the modules must be kept below plenum pressure if theability to automatically adjust the spacing between the module and theribbon is to be retained. The inlet orifices to the modules along theouter edge of wall 40 may be decreased in size to effect a greaterpressure drop between the module pressure and the common plenumpressure. Such a decrease in pressure facilitates the outward flow ofgas from the curtain where exhaust passages are not provided around eachmodule.

The temperature of the gas supplied to the front and side sections ofwall 40 in front of baffle 46a generally should approximate a meltingtemperature of the glass or at least should be high enough to avoidcooling the ribbon edges below a melting temperature.

The ribbon 14, while floating on the metal surface, advances through thechamber 28b and finally is withdrawn from the tank 18 passing throughthe seal 52. It is pulled from the tank between the traction rolls 22which may, if desired or if necessary, exact enough tension upon theribbon to keep it moving. Enough tension may be applied by these rollsto cause the ribbon to attenuate or stretch to a thinner ribbon ifdesired.

As the ribbon passes through the chamber 28b, the temperature ismaintained high enough to cause the ribbon to become molten during asubstantial distance of its path, During this time the surfaces of theribbon smooth out and the ribbon seeks an equilibrium thickness themagnitude of which is dependent upon the pressure established withinchamber 28b.

The pressure required in the chamber 28b depends upon the thicknessdesired and the external pressure, i.e., the pressure in the chamber 28eto which the edges of the ribbon extend. Where it is desired to producea ribbon thinner than the aforesaid equilibrium thickness of about 0.27inch, the pressure in the chamber 28b should be above, normally at least0.01 ounce per square inch above, that pressure at the edges of themolten ribbon, e.g., in the chamber 28C.

For example, the ribbon tends to stabilize at a thickness et/1G inchwhen the pressure differential is 0.11 ounce per square inch.

The degree of stabilization is a function of time. Con sequently, it isreadily possible to produce glass 0.125 inch in thickness simply bysizing the thickness of the ribbon at this thickness or slightly lower,subjecting the sized ribbon to the treatment herein contemplated at asuitable pressure of about 0.2 ounce per square inch, which includesimproving its surfaces, and removing the sheet before its thickness cangrow unduly.

In general, the pressure differential established between the chamber28h and that at the edge of the sheet or ribbon ranges from 0.01 to 2ounces per square inch. High differential pressures normally areunnecessary and may :be diiicult to maintain. They should be in no eventbe so high as to cause the ribbon to break and rarely are above 5 to 10ounces per square inch.

The temperature established in the forepart of the chamber 28b is amelting temperature of the glass of the ribbon. Toward the end, i.e.,beyond baille 46a, the temperature is reduced low enough to ensuredelivery of a stable ribbon which is not marred by contact with rolls tothe discharge end of the tank, for example 600 to 800 F or below.

The rate of movement of the ribbon over the pool is controlled so as toensure a smoothing of the surfaces of the ribbon and in general this isbest accomplished by bringing a section of the ribbon to molten state.

Example I A ribbon of glass of convenient width, for example 12 inchesor more, having a composition, :by weight, of 71.38 percent SiO2, 13.26percent NaZO-l-KZO, 11.76 percent CaO, 2.54 percent MgO, 0.75 percentNa2SO4. 0.15 percent A1203, 0.11 percent Fe203, and 0.06 percent NaCl,and a weight density of 2.542 grams per cubic centimeter is formed by apair of rolls to a thickness of substantially 0.125 inch and deliveredat 1400 F. and floated upon the surface of a molten bath of metal of 100percent tin having a weight density of 6.52 grams per cubic centimeterat 1800 F. The tank of molten metal is of the construction illustratedin the drawing and is longitudinally divided into three sections, anentrance section, the metal of which is maintained at a temperature of1500 F., a melting section, the metal of which is maintained at atemperature of 1900 F., and a cooling section in which the metal is at atemperature ranging from 1900 F. to 1000 F. The space above the metal issubdivided into two pressure chambers and pressurized gas is fed to eachchamber. The gas is preheated to 1900 F. for this supply. The firstchamber 28a is maintained at slightly above atmospheric pressure whilethe second chamber 28hl is maintained Iat 0.5 ounce per square inchgauge pressure, so that a pressure differential of 0.2 ounce per squareinch existed between the two chambers.

The width of the ribbon is greater than the width of the second chamberso that the margins of the ribbon extend laterally beyond the outer sideedge of the chamber. The glass is heated from above to ya temperature of1900 F. in the second chamber to remelt the ribbon throughout its entirethickness in a section across the entire width of the ribbon under thechamber and is then cooled to 1000 F. at the exit of the molten metaltank after which it is withdrawn from metal contact. The ribbonthickness remains at substantially 0.125 inch and the surfaces arefire-finished and at except for the edges which are bulbed.

The interior of chamber 281; is separated from chambers 28a and 28c ybya gas pressure seal or curtain in the manner shown in FIG. 8 of thedrawings` Gas is supplied to the plenum chamber 85 at a pressure of 10ounces per square inch gauge. Orices in the modules 80 reduce thepressure by a factor of approximately twenty times with the glass ribbonspaced approximately 0.020 inch from the outer terminal of the modules,providing a curtain or seal pressure of 0.5 ounce per square inch gaugeagainst the ribbon. Exhaust zones 86 and channels 87 allow the ow of gasfrom the curtain to escape to chamber 28C.

Various other embodiment of the process may be practiced. For example,the ribbon may be supplied substantially at melting temperature to themolten metal, held molten for a period and then gradually cooled.Pressure zones forming the uid pressure seal may be formed by othermodules or nozzles than those depicted herein while not departing fromthe principle disclosed. The fluid curtain may vary in width from `oneor two pressure zones to ve or more. The entrance and exit seals to tank18 may be constructed in the same manner as the pressure seal beneathwall 40 where improved sealing is desired. As indicated in phantom inFIG. 2 of the drawings, the central chamber 28b may be tapered to anarrower width toward the withdrawal end of the tank to maintain thefluid pressure seals in proper relationship with the marginal edges ofthe ribbon in those pvocesses wherein the ribbon is attenuated to, inpart, reduce the thickness. Such attenuation results in a narrowing, aswell as a thinning, of the ribbon.

Referring now to FIGS. 12-16, apparatus is shown for applying asuper-atmospheric pressure to the upper surface of a oating ribbon ofglass with a plurality of relatively small Huid pressure zones. The tankconstruction of this embodiment being the same as in the embodimentshown in FIG. 1, all like parts are designated with the same referencenumerals and need not be again described.

ln place of the circumferential wall 40 and uid pressure seal of modulesseparating the upper chamber 28 of tank 18 into the separate chambers ofthe embodiment shown in FIG. 1, a super-atmospheric pressure is appliedto the central area of the ribbon 14 by a bed of modules 80 overlying,in close proximity, the entire width of the ribbon, except for themarginal edges along each side, and most of the length of the lloat tankincluding the heating zone, surfacing zone and at least the lirstportion of the cooling zone. Plenum chamber is supported above theribbon in the top 28 of tank 18 by cross beams .suitably fastened to thesides of tank 18. Inert gas under pressure is supplied to each module 80from an associated plenum chamber 85 subdivided into independentsubplenums by barrier 88'. Each subplenum is supplied with inert gas,such as nitrogen under pressure, through pipes 89 from a source, notshown. The gas is preheated to approximately the temperature of theglass before being introduced to the plenum chamber and radiant heaters48 maintain the temperature.

Each module is small with respect to the length and width of the ribbonand is close to, but spaced from, the next adjacent m-odules. In theembodiment shown, all modules 80 have their lower termini of rectangularconfiguration and lying in a common plane. The modules 80 are arrangedin successive rows crossing the intended path of travel of the ribbon.Preferably, the rows are at an angle from the direction of ribbontravel, as illustrated in FIG. 13. Each module is subdivided into aplurality of separate chambers 80a', 80b, 80C', and 80d', eachindividually supplied with gas through orices 82.

Each module 80 has a hollow stem 84 of smaller cross sectional area thanthe outer terminus and each opens into a plenum chamber 85 positionedabove the module bed and acting as a support therefor. Each module 80'is substantially enclosed, except .for the lower, open end, andseparated from other modules by an exhaust zone 86 communicating withlarger exhaust channels 87 between the module stems. Tubes communicatebetween exhaust channels 87 and the surrounding atmosphere and prevent apressure build-up in the exhaust spaces. Exhaust gases also ilowlaterally along channels 87 to the marginal edges of the plenumchambers.

In operation, the individually supplied pressure zones functionindependently from one another in the same manner as in theaforedescribed fluid pressure seal. Thus, the combination of the smallorifices 82 and the Iclose spacing, generally 0.001 to 0.10 inch,between the lower termini of the module walls and the glass ribbonprovides a self-adjusting gap therebetween that assures the existence ofa uniform pressure over the entire ribbon beneath the module bed andhence a uniform thickness.

Exhaust zones such as those provided by passageways 86 between adjacentpressure zones beneath modules 80 are necessary to prevent a build-up ofpressure centrally of the ribbon. Such a build-up is caused when gasmust flow laterally across the ribbon to exhaust at the marginal edges.A nonuniform pressure of this type would cause the ribbon to be thin inthe center and progressively thicker toward the sides. The uniformpressure beneath each module and the overall flatness of the pressureprofile beneath the entire module bed is diagrammatically indicated bythe graphs accompanying FIG. 16. Uniformity of treatment is furtherassu-red by skewing the module rows relative to the path of ribbontravel. With such an arrangement no one portion of the ribbon travelsunder an exhaust zone for any appreciable distance, and any variationsin pressure or temperature are averaged throughout the ribbon.

Where desired, the transversely extending subplenums may be suppliedwith gas at different pressures. Thus, a high initial pressure may bedesirable to rapidly bring the glass ribbon to a proper thickness whilea lower pressure thereafter will maintain this thickness. Adequateexhaust space between adjacent modules allows purposely createddifferential pressures to exist throughout the module bed by essentiallyisolating one pressure zone from the next.

For special purposes, it may be desirable to vary the pressuretransversely of the ribbon and thereby vary the thickness at whichvarious portions of the ribbon stabilize. This can be accomplished bysubdividing the plenum chamber 85 longitudinally of the ribbon travelinto as many subplenums as desired. It may also be accomplished byvarying the size of lthe orifices 82 in the manner described inconnection with the fluid pressure seal formed with modules 80. Byprogressively varying the pressure across the width of the ribbon, aribbon of glass wedge shaped in transverse cross section can beproduced. This can also be achieved by progressively varying the spacingbetween the lower extremities of Ithe modules and the ribbon, as byslightly tilting the module bed transversely of the ribbon. Of course,the variation in thickness across the width need not be progressive butcan abruptly change in stages to produce a series of contiguous stripsof different thicknesses, each strip being a constant thickness. Othervariations will occur to those skilled in the art. Such glass would finduse as an architectural product.

The embodiment shown in FIGS. 17 and 18 may also be used to apply asuper-atmospheric pressure above the oating ribbon 14. A porous plate102 forms the bottom of a plenum chamber 104 and extends above andclosely spaced from ribbon 14 in -the same manner as the bed of modules80'. The porous plate 102 may be made of porous stainless steel or otherheat resistant foraminous material. By virtue of the large number ofsmall, randomly located passageways through plate 102, the plenumpressure is reduced and the flow of gas diffused to provide a uniformpressure on the ribbon. Tubes 106 open through the porous plate 102 andextend through the plenum chamber 104, opening to the atmosphere above,thereby providing exhaust channels for the flow of gas emitted throughthe pores of plate 102. This prevents a build-up of pressure centrallyof the ribbon and assures a uniform pressure profile across the width ofthe ribbon. Such a plenum chamber having a porous wall and exhaustpassages is disclosed and claimed in the copending application of GeorgeW. Misson, Ser. No. 251,851, filed Jan. 16, 1963, now Patent No.3,300,290.

Example II A ribbon of glass of convenient width, for example 12 inchesor more, having a composition, by weight, of 71.38 percent SiOZ, 13.26percent Na2O-l-K2O, 11.76 percent CaO, 2.54 percent MgO, 0.75 percentNa2SO4, 0.15 percent A1203, 0.11 percent Fe203, and 0.06 percent NaCl,and a weight density of 2.542 grams per cubic centimeter is formed by apair of rolls to a thickness of substantially 0.125 inch and deliveredat 1400 F. and floated upon the surface of a molten bath of metal of 100percent tin having a weight density of 6.52 grams per cubic centimeterat 1800 F. The tank of molten metal is of the construction illustratedin the drawing and is longitudinally divided into three zones: anentrance zone, the metal of which is maintained at a temperature of 1500F.; a heating zone, the metal of which is maintained at a temperature of1900" F.; and a cooling zone in which the metal is at a temperatureranging from 1900 F. to 1000 F. The chamber above the metal ismaintained at a pressure slightly above atmospheric by introducing aninert gas at a slight positive pressure of about 0.2 ounce per squareinch and preheated to 1900 F.

A module bed is disposed above the ribbon with the lower termini of themodules spaced from the ribbon a distance of approximately 0.020 inch.Inert gas preheated to a temperature of 1900 F. is supplied underpressure to the plenum chambers in the subplenums overlying the heatingsurfacing zones and is preheated to a temperature of about 1400 F. forthe subplenum overlying the first portion of the cooling zone. The gasis supplied to all subplenums at a pressure of 10 ounces per square inchgauge. Orifices in the modules reduce the pressure by a factor ofapproximately twenty times with the underlying glass spaced from themodule walls a distance of about 0.020 inch. A pressure of approximately0.50 ounce per square inch gauge is uniformly applied above that portionof the ribbon underlying the module bed.

The width of the ribbon is slightly greater than the Width of the modulebed so that the margins of the ribbon extend laterally beyond the bed.The glass is heated from above by the hot gas from the modules and fromradiant heat to a temperature of 1900 F. in the heating and surfacingzone to reheat the ribbon to a flowing condition throughout its entirethickness in a section across the entire width of the ribbon beneath themodule bed. The ribbon is then cooled to 1000 F. in the cooling zone atthe exit end of the molten metal tank, after which it is withdrawn frommetal contact. The ribbon thickness remains at substantially 0.125 inchand the surfaces are fire-finished and at except for the edges which arebulbed.

Although the present invention has been described with reference tocertain specific details, it is not intended that such details shall beregarded as limitations upon the scope of the invention except insofaras included in the accompanying claims.

We claim:

1. In a process of producing glass sheet wherein the glass is depositedupon and supported on a liquid having a density greater than that of theglass and the glass when 4molten and allowed to How freely on saidliquid tends to naturally attain an equilibrium thickness, theimprovement which comprises,

floating a layer of glass at a temperature at which it flows on saidliquid, flowing a pressurized gas from a plurality of spaced andseparate pressure zones onto laterally spaced areas of the upper surfaceof the glass beneath said zones located above each of said areas andwithin the edges thereof, flowing the gas at different pressures fromdifferent zones above each said area, maintaining the pressure of thezones above the most Closely adjacent portions of said laterally spacedareas at a first pressure which is substantially the same as thepressure between said laterally spaced areas, maintaining the pressureof the zones above the most remote portions of said laterally spacedareas at a second pressure which is substantially the same as thepressure beyond said laterally spaced areas and above said supportingliquid, and

maintaining a gradient in the pressures provided by the laterally spacedpressure zones located between each pair of said pressure zonesproviding said rst and second pressure,

whereby to subject liquid outside and in contact with the glass to aiiuid pressure of different magnitude than that of said gas between saidlaterally spaced areas to control the thickness of the glass within theedges thereof so as to be different from said equilibrium thickness.

2. In a process of producing glass sheet wherein the glass is depositedupon and supported on a liquid having a density greater than that of theglass and the glass when molten and allowed to flow freely on saidliquid tends to naturally attain an equilibrium thickness, theimprovement which comprises,

oating a layer of glass at a temperature at which it flows on saidliquid, flowing pressurized gas at a uniform pressure upon the area ofthe glass supported on said liquid from a plurality of spaced andseparate pressure zones arranged in a row extending transverse to thelength of the glass sheet at a location closely adjacent that at whichsaid glass is deposited upon said supporting liquid, flowing pressurizedgas upon the area of the glass supported on said liquid from each of thetransversely arranged zones in each of a plurality of rows of zonesarranged sequentially lengthwise of said glass sheet and beyond saidfirst-named row, maintaining the pressure of the gas uniform in each ofthe transversely arranged pressure zones in each row,

maintaining the pressure of the gas from each such row at a value lessthan that of the preceding row,

maintaining the pressure of the gas from the row of transverselyarranged zones most remote from the location at which said glass isdeposited on said supporting liquid at a value suicient to maintain saidglass at a predetermined thickness,

maintaining pressurized gas over the supporting liquid outside and incontact with the glass to provide a gas pressure thereover of adifferent magnitude than that of said gas between said pressure zonesand the surface of the glass therebelow,

whereby said glass deposited on said supporting liquid rapidly reachesits predetermined thickness provided for by said diiference in magnitudeof the gas pressures over said glass and said liquid outside and incontact with said glass. 3. In a process of producing glass sheetwherein the glass is deposited upon and supported on a liquid having adensity greater than that of the glass and the glass when molten andallowed to flow freely on said liquid tends to naturally attain andequilibrium thickness, the improvement which comprises,

floating a layer of glass at a temperature at which it flows on saidliquid, owing pressurized gas upon the area of the glass supported onsaid liquid from a plurality of rows of spaced and separate pressurezones extending transversely to the length of the glass sheet, said rowsof said zones being arranged adjacent to one another and extendinglengthwise of said glass sheet,

maintaining the pressure of the gas from pressure zones lying on oneaxis extending lengthwise of said glass sheet at a Value different thanthat from pressure zones lying on a second axis extending lengthwise ofsaid glass sheet and spaced laterally from said rstnamed axis, and

maintaining pressurized gas over the liquid outside and in contact withthe glass to provide a gas pressure thereover of a different magnitudethan that of said gas between said pressure zones and the surface of theglass therebelow,

whereby to produce a glass sheet having laterally spaced zones ofdifferent thickness extending lengthwise of said sheet.

4. The process of claim 3 wherein the pressure of the gas owing fromeach separate pressure zone is uniformly and transversely, progressivelyless in each row of said zones transversely of said glass sheet,

whereby to produce a glass sheet having a wedgeshaped cross sectionextending transversely of the lengthwise direction of said glass sheet.

References Cited UNITED STATES PATENTS 2,911,759 11/ 1959 Pilkington etal. n- 65-182 3,048,383 S/l962 Champlin 65-182 3,223,501 12/ 1965Fredley et al 65-182 3,241,939 3/ 1966 Michalik 65-99 FOREIGN PATENTS732,043 2/ 1943 Germany.

DONALL H. SYLVESTER, Primary Examiner. D. CRUPAIN, G. R. MYERS,Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No.5,345,149 october 3, 1967 Edmund R. Mchalik et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 13, line 8, for "pressure" read pressures column 14, line 7, for"and" read an Signed and sealed this 19th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. IN A PROCESS OF PRODUCING GLASS SHEET WHEREIN THE GLASS IS DEPOSITEDUPON AND SUPPORTED ON A LIQUID HAVING A DENSITY GREATER THAN THAT OF THEGLASS AND THE GLASS WHEN MOLTEN AND ALLOWED TO FLOW FREELY ON SAIDLIQUID TENDS TO NATURALLY ATTAIN AN EQUILIBRIUM THICKNESS, THEIMPROVEMENT WHICH COMPRISES, FLOATING A LAYER OF GLASS AT A TEMPERATUREAT WHICH IT FLOWS ON SAID LIQUID, FLOWING A PRESSURIZED GAS FROM APLURALITY OF SPACED AND SEPARATE PRESSURE ZONES ONTO LATERALLY SPACEDAREAS OF THE UPPER SURFACE OF THE GLASS BENEATH SAID ZONES LOCATED ABOVEEACH OF SAID AREAS AND WITHIN THE EDGES THEREOF, FLOWING THE GAS ATDIFFERENT PRESSURES FROM DIFFERENT ZONES ABOVE EACH SAID AREA,MAINTAINING THE PRESSURE OF THE ZONES ABOVE THE MOST CLOSELY ADJACENTPORTIONS OF SAID LATERALLY SPACED AREAS AT A FIRST PRESSURE WHICH ISSUBSTANTIALLY THE SAME AS THE PRESSURE BETWEEN SAID LATERALLY SPACEDAREAS, MAINTAINING THE PRESSURE OF THE ZONES ABOVE THE MOST REMOTEPORTIONS OF SAID LATERALLY SPACED AREAS AT A SECOND PRESSURE WHICH ISSUBSTANTIALLY THE SAME AS THE PRESSURE BEYOND SAID LATERALLY SPACEDAREAS AND ABOVE SAID SUPPORTING LIQUID, AND MAINTAINING A GRADIENT INTHE PRESSURES PROVIDED BY THE LATERALLY SPACED PRESSURE ZONES LOCATEDBETWEEN EACH PAIR OF SAID PRESSUE ZONES PROVIDING SAID FIRST AND SECONDPRESSURE, WHEREBY TO SUBJECT LIQUID OUTSIDE AND IN CONTACT WITH THEGLASS TO A FLUID PRESSURE OF DIFFERENT MAGNITUDE THAN THAT OF SAID GASBETWEEN SAID LATERALLY SPACED AREAS TO CONTROL THE THICKNESS OF THEGLASS WITHIN THE EDGES THEREOF SO AS TO BE DIFFERENT FROM SAIDEQUILIBRIUM THICKNESS.